The present invention relates to a hybrid drive unit.
In recent years, by combining an engine and rotary electric machines, hybrid vehicles that can enable the engine to improve fuel economy and to reduce exhaust emission have come into practical use. As an example of a hybrid drive unit used for such a hybrid vehicle, there exists a hybrid drive unit that includes an input shaft connected to an engine, an output shaft connected to wheels, a first rotary electric machine, a second rotary electric machine, a power distribution device for distributing a rotational driving force of the input shaft to the output shaft and to the first rotary electric machine, and a transmission device connected between the second rotary electric machine and the output shaft (refer, for example, to Japanese Patent Publication No. JP-3807386). In this hybrid drive unit, the transmission device is structured to have a plurality of shift speeds. By changing a rotation speed of the second rotary electric machine by a speed ratio corresponding to a rotation speed of the output shaft, the transmission device transmits the rotation speed to the output shaft.
In addition, in this hybrid drive unit, a high-speed mode is selected when a vehicle speed exceeds a predetermined value and also a requested torque is less than a predetermined value. Furthermore, this high-speed mode includes a normal mode and a cruise mode, and the cruise mode (high-speed cruise mode) is selected during a low load in which the requested torque to the second rotary electric machine is zero or less. In this high-speed cruise mode, a rotor of the first rotary electric machine is fixed by a brake, and also a brake of the transmission device is released to allow a rotating member of the transmission device disposed between the output shaft and the second rotary electric machine to run idle. Power is thus hardly transmitted between the output shaft and the second rotary electric machine.
Moreover, this hybrid drive unit is provided with a structure for minimizing the generation of a power loss (drag loss) caused by transmission of engine power, though a small quantity, to the second rotary electric machine and to the rotating member of the transmission device in the high-speed cruise mode as described above. In other words, this hybrid drive unit includes a judgment unit for judging an energy of the drag loss, and a control unit for controlling a rotation speed of the second rotary electric machine based on a judgment result by this judgment unit. In addition, this hybrid drive unit is structured to minimize the power loss of the hybrid drive unit by controlling the rotation speed of the second rotary electric machine so as to minimize the drag loss energy in the high-speed cruise mode.